Piles of Granular materials blown into walls

Topic: Granular Materials

Research Questions:
The primary idea behind this research is to see what the behavior and properties of wind-blown granular materials, such as sand or small beads, when those grains are i) blown from a pile, and ii) when those same grains collide with a wall not far away from the pile. There are numerous specific questions one can address with a system such as this, as listed below.

Try to make observations of how the pile is actually blown away. Do grains begin to be blown off the pile from the side closest to the fan, from the sides, or from the side farthest from the fan? Then, when grains hit the wall, what is the distribution of the grains as they land and begin to pile up again? Are there patterns and consistencies you observe if you do a number of trials? Is there any avalanching on either end of the process?


Materials and Methods Outline:
You will need some sort of fine granular material. This can be sand, small spherical beads of bronze, copper, or other material. You will need some type of fan that can have a focused stream of blown air. Perhaps a hair dryer or shopvac. It is ideal to have something that has multiple options for wind speed.

The other main piece of equipment will be some sort of camera that has video capabilities. Video will be the main method of collecting data and making measurements. The key to making measurements from video is to have a ruler of some type in the video, which can be used to make calibrations within a program such as Tracker or LoggerPro. If you have access to any video hardware with high-speed options, such as on an iPhone 6 or many other cameras (instead of the standard 30 frames per second (fps), some can be turned to 60 fps, 120 fps, 240 fps, or even 480 fps or 1000 fps); note that the clarity and resolution of video gets worse with higher fps values - you will need to experiment with the settings to get the optimal balance for frame rate and clarity to get measurements you trust.

Specific Research Questions can include:

• Decomposition of pile as a function of airspeed from the fan or hair dryer/blower
• How does changing the angle of airstream as it hits the pile affect decomposition?
• The height of the pile
• The diameter of the pile
• The slope of the pile
• The size of the grains making up the pile
• If the pile is a random mix of two or more sizes of grains
• If there is a small pile of one size grain, buried below another size grain
• Effect of different sized, shaped obstacles between wind source and granular pile
• What are the characteristics of any pile formed at the wall?
• Any difference(s) between a straight wall and a curved wall?
• What happens if the wall is tilted at difference angles? 
• Change the material of the wall (coefficient of restitution between grain and wall)
• How does the pile change as a function of distance between the pile and the wall?
• What is there are two piles side by side?
• What if a second pile is in between the first pile and the wall? 
• If two different grains are used, is there any segregation and/or stratification in the pile that is formed? 
• Is there avalanching of any kind on either side of the original pile(s)? In the formed pile at the wall?
• Instead of symmetric pile (more coned shaped), what is the pile is a ramp with a flat end? Try piles of different geometric shapes.

Related articles and links in the literature (if you do not have access to an article, email us at vondracekm@eths202.org):

- Transport by wind of granular materials of different grain shapes and densities

- Determination of wind induced detachment threshold for granular material on Mars